Field coil bobbin for electric drills



Sept. 29, 1936. F, FOVRSS4 2,055,861

FIELD COIL BOBBIN FOR ELECTRIC DRILLS Filed Oct. 18, 1955 INVENTOR.

R/TH/OF E F0R55 BY (W 1 1 ATTORNEYJ Patented Sept. 29, 1936 FIELD COIL BOBBIN FOB ELECTRIC DRILLS Frithiof P. Forss, Aurora, 111., assignor to Independent Pneumatic Tool (10., Chicago, 111., a corporation of Delaware Application October 18, 1935, Serial No. 45,541

7 Claims. (01. 172-36) This invention relates to relatively small portable electric hand drills of the gun or pistol type. This drill is held in and supported by one hand grasping the body of the drill on opposite sides and the single handle at rear end of the drill. The handle is of the pistol grip type and is preferably made hollow to provide an air duct for the cooling system for the motor and to accommo date one of the brushes of the motor which is of the horseshoe type and also the connector by which said brush is electrically attached to one of the current supply wires for the tool.

The motor being of the horseshoe type has its field coil in laterally offset relation to its armature. The motor is preferably arranged in the drill casing to have its armature in the lower portion of the casing and its field coil in the upper part of said casing. The snap switch which is operable by the thumb of the hand grasping the drill to control the supply of electric current to the motor is located in thedrill casing above the armature and to the rear of the field coil in the space between said coil and the upper brush of the motor, which brush is also located above the armature. The switch device is closely adjacent the upper brush and the field coil, respectively, and has outside contacts on the opposite sides of its case for electrical connection with said brush and coil.

The general purpose and object of my invention is to provide the field coil at its end adjacent the switch device with a contact strip or bar extending across the end of the field coil in position to be directly engaged by the opposed contact of the switch device on inserting the latter into the drill casing. The switch device is inserted endwise into the drill casing and the contact strip extends along this direction of movement and in the path of the switch contact so that the two may have direct contact on sliding the switch, device in place in the drill casing.

A further object of my invention is to have the contact strip span and engage the adjacent end of the insulation bobbin of the field coil for holding the strip in place.

A further object of my invention is to provide the bobbin with spaced lugs to provide channels to receive the bent over ends of the contact strip, thus centering the strip onv the bobbin and providing an interlocking connection between the strip and the bobbin.

The invention consists further in the matters hereinafter described and claimed.

In the accompanying drawing showing one embodiment of my invention;

Fig. 1 is a side view of a small portable electric hand drill provided with a contact strip and bobbin arrangement in accordance with my invention, the motor casing of the drill being broken away and parts being in section respectively to 5 illustrate the construction;

Fig. 2 is a top plan view'of a portion of the drill shown in Fig. 1 with the motor case in section to more clearly show the features of my invention;

Fig. 3 is a perspective view of the two parts of 10 the bobbin in disassembled relation;

Fig. 4 is a sectional view with parts in elevation taken on line 4-4 of Fig. 1; and

Fig. 5 is a perspective view showing the manner in which one of the external contacts of the 15 switch device engages the field coil contact bar or strip to be hereinafter described.

In the drawing, l indicates the outer casing of the drill enclosing the electric motor which furnishes the power for turning the chuck shaft or 20 spindle 2. The motor is of the horseshoe type and is mounted in the drill casing l with its field coil 3 in the upper portion of the casing and its armature 4 in the lower part of said casing. This disposes the field pieces5 of the motor on opposite sides of the armature as indicated in Fig. 2.

The handle 6 of the tool is of the pistol grip type and extends below the case I in approximately normal relation thereto as shown. The handle is located at the rear end of the drill and is hollow as heretofore described.

The switch device I by which the electric current supply to the motor is controlled is mounted in the drill case I above the armature 4 and in juxtaposition to the rear end of the field coil 3 as shown in the drawing. The switch device is of the snap type and is provided with an operating button 8 accessible at one side of the drill casing adjacent the handle as shown in Fig. 2.

The field coil 3 comprises a bobbin, which as shown in Fig. 3, is composed of a pair of substantially similar, separable sections 9, Ill. The latter are made of a suitable electrical insulating material, preferably of a character light in weight and which can be die cast. The sections 9, l0 have side and end flanges providing channels, which when the sections are assembled, receive the field winding H. The latter encompasses the sections and holds them assembled with their body walls i 2, l2 in spaced relation to accommodate the yoke l3 of the field pieces 5, 5, as shown in Figs. 1 and 2.

The end walls l4, M of the sections 9, l0 and the end flanges l5, iii of said sections extend to one side of the body walls l2.of the sections and engage along their meeting edges to space said body walls and to support the sections in assembled relation. The end flanges I5, I6 join the side flanges on the opposite sides of the body walls I2 and continue the channels, heretofore referred to, about the ends of the sections.

The switch device 1, that is, the insulation casing of said device, is provided on its opposite sides with contacts, one for connecting the switch device with the upper brush (not shown) of the motor, and the other contact to connect the switch device with the winding II of the field coil 3. The last mentioned contact is shown at I1 in Figs. 1 and 2. This contact is in the form of a metal plate seated in a channel in the side of the switch casing and having a struck out tongue I8 to yieldably engage a contact strip or bar I9 at the adjacent end of the field coil 3.

The contact strip I9 spans the end of the bobbin and has interlocking and centering connection with the sections 9, I0 thereof. For this purpose, the bobbin sections have outwardly projecting substantially parallel ribs 20, on its end fianges I5. Each bobbin section has a pair of these ribs, one on each end flange, as

shown. The ribs, when the bobbin sections are assembled provide channels to receive the bent -over ends of the contact strip I9, as illustrated herein. These channels are as wide as the strip, and thus the ribs center the strip on the bobbin, and position the strip in the path of the tongue I8 for direct contact therewith on inserting the switch device in the drill casing I. The latter has aligned openings 2I in its side walls to receive the switch device. The latter is slid end wise into the drill case, and the contact strip I9 extends in the direction of this movement. The strip I9 is connectedat one end with the field winding II, as at 22 in Fig. 2.

The main advantage of the contact strip arrangement is that the switch device is connected with the field coil on merely sliding the switch device into the drill casing. This facilitates assembling and disassembling the tool and also simplifies the construction. 7

The drill shown has a free speed of approximately 2500 R. P. M. and operates on the usual commercial electric current of 110 volts. The motor is of the universal type, operating on either a D. C. or an A. C. current. The drill is relatively small and light in weight. It is held in one hand, and being small may be used in close quarters to drill at any desired angle.

The shaft of the armature 4 is journaled at its opposite ends in the casing of the tool as in devices of this character and moreover the fore end of said shaft has a driving connection with the spindle 2 for turning the chuck in the operation of the tool. This driving connection may comprise a meshing pinion and gear on the armature and chuck shafts, respectively. This gearing is located at the forward end of the drill in the gear housing which is removably secured to the casing I by screws as shown. The shaft 2 is located in oflset relation to the axis of the armature 4 on the side of said axis opposite the handle 6. The cooling system for the drill includes a rotary fan in the casing I, said fan being fixed to the armature shaft for rotation therewith. The fan draws cooling air into the casing I throughthe hollow handle 6 which has an intake opening for that purpose at its lower or outer end. The fan discharges the air out of the casing through one or more vent holes as shown in Fig. l.

The details of construction and arrangement of parts shown and described may be variously changed and modified without departing from the spirit and scope of my invention, except as pointed out in the annexed claims.

A spare brush holder 23 is mounted in the easing I at the forward end of the field coil as shown in Figs. 1 and 2. A screw plug 24 closes the outer end of the holder. The latter extends across the front end of the bobbin as'shown and must be removed before the stator assembly can be slid out of the casing I. One brush for the motor is located in the handle 6. The other brush is located in the casing I above the handle and its holder, as shown in Fig. 4, has interlocking connection with the casing of the switch device 1 to removably hold the latter in place in the casing I. The upper brush holder has its upper end engaged by a plug 25 screwed into the casing above the holder for holding the latter in place in the drill casing. As illustrated in Fig. 4, the upper brush holder comprises a metal tube 26 tightly fitted in an outer sleeve 21 of insulating material and exposed along one side of the sleeve for direct engagement with a spring contact finger 28 struck out from a metal contact plate 29 fitted in a channel 30 in the side of the switch casing 1 adjacent the brush holder. The sleeve 21 has a sliding fit in a channel shaped-member 3| castintegral with the outer case I to hold the upper brush in position in said outer case. The sleeve 21 extends into the channel 30 to interlock with the switch device 1 when the parts are assembled. This engagement is made after the switch device has been inserted into the drill case I through the openings 2I. To release the switch device for removal from the drill case I, the plug 25 is removed and the upper brush holder is then slid out of the drill case to unlock the switch device.

The manner in which the contact strip or bar IQ of the field coil bobbin engages the tongue I8 on the side of the switch case 1 opposite the upper brush holder is clearly shown in Fig. 5. As illustrated, the tongue I8 projects sumciently outward from the channel 32 in the switch case 1 to yieldably engage against the bar I9 on inserting the switch device into the tool casin through one of the openings 2 I.

As indicated in the drawing, and more particularly in Figs. 4 and 5, the casing of the switch device 1 is made in two longitudinally separable parts 1a, 1a'which parts are secured together by'a single fastening bolt 1b.

The upper and the lower brushes, each comprise a carbon rod slidably mounted in the metal tube of its brush holder sleeve and urged into contact with the commutator of the motor by a coiled spring; The opposite ends of the spring seat against the carbon rod and the closure cap for the brush holder, respectively. In Fig. 4 the carbon rod is marked 33 and the spring 34.

The construction of the two part switch casing 1 embodying the single fastening element 1b and the feature of the spring contacts on opposite sides of the switch casing to yieldably engage the associated brush holder and field coil contacts when the switch device 1 is in place in the tool, as disclosed herein. constitutes the subject matter of the co-pending application of Frank B.

I claim as my invention:

1. In a portable electric tool of the character described, an outer casing, a horseshoe type motor therein, a control switch for the motor, said switch device being removably mounted in the casing adjacent the field coil of the motor, and cooperating contacts on the switch device and the coil, respectively, said contacts having surface engagement for electrically connecting the switch device and the coil on inserting the switch device in the casing.

2. In a portable electric tool of the character described, an outer casing, a horseshoe type motor therein, a control switch for themotor, said switch device being removably mounted in the casing adjacent the field coil of the motor, and cooperating contacts on the switch device and the coil, respectively, said contacts having surface engagement, one of said contacts being in the form of a strip extending in the direction of movement of the switch device into the outer casing for electrically connecting the coil and the switch device on inserting the latter in the casing.

3. In a portable electric tool of the character described, an outer casing, a horseshoe type motor therein, said motor having a field coil comprising a winding and an insulating bobbin supporting the same, a control switch for the motor, said switch device being slidably mounted in the casing adjacent the field coil, an exterior contact on the switch device, and a contact strip carried by the bobbin and connected with the coil winding, said contact strip extending in the direction of movement of the switch device into the casing and engageable with the contact on the switch device on inserting the latterin the casing. 4. In a portable electric tool of the character described, an outer casing, a horseshoe type motor therein, said motor having a field coil comprising a winding and an insulating bobbin supporting the same, a control switch for the motor, said switch device being slidably mounted in the casing adjacent the field coil, an exterior contact on the switch device, and a contact strip connected with the coil winding and spanning the end of the bobbin adjacent the switch device i'or engagement with the contact of the switch device on inserting the latter in the casing. 5. In a field coil for a horseshoe type motor, a coil winding, an insulating bobbin for supporting the winding, said bobbin comprising a pair of substantially similar separable sections, said sections having side and end flanges providing a channel for the coil winding, a. contact strip spanning one end of the bobbin and connected with the coil winding, said strip having its ends bent to engage the associated flanges of the bobbin sections, and means providing an interlocking connection between the contact strip and the bobbin sections.

6. In a field coil for a horseshoe type motor, a coil winding, an insulating bobbin for supporting the winding, said bobbin comprising a pair of substantially similar separable sections, said sections having side and end flanges providing a channel for the coil winding, a contact strip spanning one end of the bobbin and connected with the coil winding, said strip having its ends bent to engage the associated flanges of the bobbin sections, and ribs on the sections providing grooves to receive the bent ends of the strip.

7. In a portable electric hand tool of the character described, an outer casing, a grip handle at the rear end of the casing and extending below the same, a horseshoe type motor located in the casing forward of the handle with the armature of the motor in the lower part of the casing and the field coil of the motor in the upper part of the casing, a control switch for the motor, said switch device being slidably mounted in the casing above the armature between the handle and. the rear end 01' the field coil, and cooperating contacts on the switchdevice and the coil, respectively, for electrically connecting the switch .device to the coil on inserting the switch device in the easing.

FRITHIOF P. FORSS. 

